Method and device for welding an aluminum-based stud

ABSTRACT

A method of welding a stud ( 11 ) is provided. In another aspect of the present invention, a welding system is provided for a weld stud ( 11 ). A further aspect of the present invention employs a weld stud ( 11 ) with a substantially conical end section ( 29 ). Still another aspect of the present invention includes a welding method, wherein an aluminum or aluminum alloy stud ( 11 ) is brought into contact with an aluminum or aluminum alloy base material ( 14 ), voltage is applied between the stud ( 11 ) and the base material ( 14 ), the stud ( 11 ) is lifted slightly off the base material ( 14 ), an arc is generated, the tip of the stud ( 11 ) and the section of the base material ( 14 ) to be melted are melted, pressure is applied to the tip of the stud ( 11 ) and the section of the base material ( 14 ) that has been melted and the stud ( 11 ) and base material ( 14 ) are welded together, the current is divided into at least three stages and incrementally increased from the beginning to the end while the main arc is generated, and/or the molten tip of the aluminum or aluminum alloy stud ( 11 ) is applied under pressure to the molten base material ( 14 ) in under five milliseconds after the arc current has been cut off.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a method and device for welding analuminum or aluminum alloy stud and, more specifically, to a weldingmethod and device in which a stud is brought into contact with a basematerial, voltage is applied between the stud and the base material, thestud is lifted slightly off the base material, an arc is generatedbetween the stud and the base material, the tip of the stud and thesection of the base material to be melted are melted, pressure isapplied to the tip of the stud and the section of the base material thathas been melted, and the stud and base material are welded togetherafter the current has been cut off.

In a well known method, a stud is brought into contact with a basematerial, voltage is applied between the stud and the base material, thestud is lifted slightly off the base material, an arc is generatedbetween the stud and the base material, the tip of the stud and thesection of the base material to be melted are melted, pressure isapplied to the tip of the stud and the section of the base material thathas been melted, and the stud and base material are welded togetherafter the current has been cut off. In Japanese Utility ModelApplication Disclosure No. 5-49172 and Japanese Utility ModelApplication Disclosure No. 6-48967, a pilot arc with a small amount ofcurrent is generated, the main arc with a large amount of current isgenerated, the tip of the stud and the section of the base material tobe melted are melted, pressure is applied to the tip of the stud and thesection of the base material that has been melted and the stud and basematerial are welded together (the so-called drawn arc method). Inautomobile manufacturing, aluminum and aluminum alloy vehicle frames andbodies are also increasingly being used because of their lighter weight.In Japanese Utility Model Application No. 63-173583, a T stud consistingof a large-diameter head and a rod-shaped shaft is welded to a vehicleframe, and a clip for securing a member such as wiring is fastened tothe T stud.

Technologies have already been developed to weld T studs to vehiclebodies and frames when the bodies and the T studs are made fromiron-based metals. In these welding technologies, the T stud is weldedto the body or frame while maintaining a constant level of strength. Forexample, when the iron-based T stud 1 in FIG. 1 has a 5-mm diameter head2 and a 3-mm long, 3-mm diameter rod-shaped shaft 3, the height of thestud 1 below the neck after being welded to a base material 5 such as aniron-based body is about 2.6 mm, the reinforcing height (h) of thereinforcement 6 is less than 1 mm, and the diameter (d) of thereinforcement 6 is less than 5 mm. In this way, enough space remains onthe shaft 3 of the molten T stud 1 to accommodate the clip disclosed inJapanese Utility Model Application Disclosure No. 63-173583, and attachthe clip properly and securely.

However, this technology was developed to weld an iron-based T stud toan iron-based base material. When the base material of the body or frameconsists of an aluminum-based metal such as aluminum or an aluminumalloy, it is difficult to weld an iron-based T stud to it. If a studconsisting of an aluminum-based metal such as aluminum or an aluminumalloy is welded in the same manner as an iron-based stud, the properheight below the neck, reinforcing height, and welding spot diametercannot be reliably obtained. In addition, the strength after weldingvaries and a stable welding strength cannot be obtained. Therefore, thepurpose of the present invention is to provide a stud welding method anddevice able to reliably obtain the desired welding profile and weldingstrength even when the stud is made from aluminum or an aluminum alloy.

In accordance with the present invention, a method of welding a stud isprovided. In another aspect of the present invention, a welding systemis provided for a weld stud. A further aspect of the present inventionemploys a weld stud with a substantially conical end section. Stillanother aspect of the present invention includes a welding method,wherein an aluminum or aluminum alloy stud is brought into contact withan aluminum or aluminum alloy base material, voltage is applied betweenthe stud and the base material, the stud is lifted slightly off the basematerial, a pilot arc with a small amount of current is generated, themain arc with a large amount of current is generated, the tip of thestud and the section of the base material to be melted are melted,pressure is applied to the tip of the stud and the section of the basematerial that has been melted and the stud and base material are weldedtogether, and the current is divided into stages and incrementallyincreased as the main arc is generated from beginning to end, and/or themolten tip of the stud is applied under pressure to the molten basematerial in under five milliseconds after the main arc current has beencut off.

The present invention also includes a welding device, wherein analuminum or aluminum alloy stud is brought into contact with an aluminumor aluminum alloy base material, voltage is applied between the stud andthe base material, the stud is lifted slightly off the base material, apilot arc with a small amount of current is generated, the main arc witha large amount of current is generated, the tip of the stud and thesection of the base material to be melted are melted, pressure isapplied to the tip of the stud and the section of the base material thathas been melted and the stud and base material are welded together, thecurrent is divided into stages from beginning to end and incrementallyincreased as the main arc is generated, and/or the molten tip of thestud is applied under pressure to the molten base material in under fivemilliseconds after the main arc current has been cut off. As a result,the desired height below the neck in the stud after welding (L in FIG.2) is reliably obtained, the welding strength is high, and thereinforcement height (h in FIG. 2) and the diameter of the meltedsection of the base material (d in FIG. 2) are kept within the properrange.

In another aspect of the welding device and method of the presentinvention, there are three steps and the main arc in the first step is asmall-current arc effective at removing oil from the surface andsurroundings of the section of the base material to be melted, the mainarc in the second step is an intermediate-current arc for melting thetip of the stud and the section of the base material to be melted andfor keeping the area of the section of the base material to be meltedwithin a predetermined range, and the main arc in the third step is alarge-current arc for melting the tip of the stud and the section of thebase material to be melted into each other deeply. A further aspect ofthe present invention uses a T stud having a large-diameter head and arod-shaped shaft, and the profile of the end of the shaft is conicalwith a flat tip. As a result, the arc is concentrated in the center, thereinforcement does not tilt to one side, and the height of thereinforcement is kept from getting shorter. A pilot arc is notabsolutely necessary.

Still another aspect of the present invention includes a welding method,wherein an aluminum or aluminum alloy stud is brought into contact withan aluminum or aluminum alloy base material, voltage is applied betweenthe stud and the base material, the stud is lifted slightly off the basematerial, an arc is generated, the tip of the stud and the section ofthe base material to be melted are melted, pressure is applied to thetip of the stud and the section of the base material that has beenmelted and the stud and base material are welded together, the currentis divided into at least three stages and incrementally increased fromthe beginning to the end while the main arc is generated, and/or themolten tip of the aluminum or aluminum alloy stud is applied underpressure to the molten base material in under five milliseconds afterthe arc current has been cut off. As a result, an aluminum-based studcan be welded properly.

Similarly, in still a further aspect of the present invention, a weldingdevice or system is used wherein an aluminum or aluminum alloy stud isbrought into contact with an aluminum or aluminum alloy base material,voltage is applied between the stud and the base material, the stud islifted slightly off the base material, an arc is generated, the tip ofthe stud and the section of the base material to be melted are melted,pressure is applied to the tip of the stud and the section of the basematerial that has been melted and the stud and base material are weldedtogether, the current is divided into stages and incrementally increasedfrom beginning to end as the arc is generated, and/or the molten tip ofthe aluminum or aluminum alloy stud is applied under pressure to themolten base material in under five milliseconds after the main arccurrent has been cut off. As a result, an aluminum-based stud can bewelded properly.

Various embodiments of the present invention are advantageous over priordevices. For example, because the main arc current of the presentinvention is divided into stages and increases incrementally in thiswelding method, the welding area of the section of the base material tobe melted is kept within the desired range when the tip of the stud isbeing welded to the section of the base material to be melted, the tipof the stud and the section of the base material to be melted are meltedinto each other deeply, and the heat introduced to the stud and basematerial remains constant. Because the tip of the stud is applied underpressure to the base material in less time and the short current iscontrolled during this time, the splattering of molten metal is reducedby the pinch effect (a phenomenon in which the large current flowingthrough the molten fluid constricts the fluid, the constriction reducesthe flow and lessens the constriction, and the lessening of theconstriction once again constricts the molten fluid). As a result, thedesired height below the neck in the stud after welding (L in FIG. 2) isreliably obtained, the reinforcement height (h in FIG. 2) and thediameter of the melted section of the base material (d in FIG. 2) arekept within the proper range, and high welding strength is maintained.Additional advantages and features of the present invention will becomeapparent from the following description and appended claims, taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an iron-based T stud of the prior art;

FIG. 2 is a front view of the iron-based stud in FIG. 1 after welding;

FIG. 3 is a block diagram of the circuit in the stud welding device ofthe present invention;

FIG. 4 is a front view of the aluminum-based T stud in the presentinvention;

FIG. 5 shows graphs of the timing when an arc is generated by the studwelding device of the present invention wherein (A) is a graph showingthe change in the arc current over time, (B) is a graph of the stud liftdistance over time, and (C) is a graph of the arc voltage between thestud and the base metal over time; and

FIG. 6 is a chart showing the preferred weld parameters for differentstuds and materials.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following is an explanation of working examples of the presentinvention with reference to the drawings. FIG. 3 is a block diagram ofthe circuit in a welding device 10 for welding an aluminum or aluminumalloy stud to an aluminum or aluminum alloy base material. The studwelding device 10 contains a collet 13 for holding a stud 11 at the tip,a welding gun 17 with a lift coil 15 as the lifting means for liftingthe stud 11 held by the collet 13 off the base material 14, and a powersource 18 connected to the welding gun to supply a specific amount ofpower between the stud 11 and the base material 14. It is not necessary,but the stud can also be welded in an inactive gas atmosphere such as anargon gas atmosphere. A stud-surrounding member such as a ferrule (notshown) can be installed on the collet 13 holding the stud.

A control device 19 is connected to the power source 18 and the weldinggun 17. The stud welding device 10 is a so-called drawn-arc stud weldingdevice in which a stud 11 is brought into contact with a base material14, voltage is applied between the stud and the base material, the studis lifted slightly off the base material, a pilot arc with a smallamount of current is generated, the main arc with a large amount ofcurrent is generated, the tip of the stud 11 and the section of the basematerial 14 to be melted are melted, pressure is applied to the stud andthe section of the base material that has been melted and the stud andbase material are welded together. Therefore, the control device 19 hasto control the supply of power from the power source 18 to the weldinggun 17 so a pilot arc and subsequent main arc are formed between thestud 11 and the base material 14. It also has to operate the lift coil15 in the welding gun 17 so the stud 11 is lifted off the base material14 to a specific height and the pilot arc and subsequent main arc aregenerated. After a certain amount of time, the lift coil 15 has to beturned off so the stud 11 is brought into contact with the base material14 forcibly. In the present invention, a drawn-arc welding device inwhich a pilot arc precedes a main arc does not have to be used. Anywelding device that generates an arc between the stud and base materialfor arc welding can be used. In the following explanation of the workingexample, however, a drawn-arc stud welding device is used.

The control device 19 has an arc voltage detector 21 for detecting thevoltage between the stud 11 and the base material 14 and outputting asignal depending on whether the stud is in contact with the basematerial or lifted off the base material. It also has a current detector22 for detecting the welding arc current supplied from the power source18 to the welding gun 17. The detection signals outputted from detectors21 and 22 are sent to a sequence controller 23 for controlling thesequence of operations required to perform stud welding. The output fromthe current detector 22 is in-putted to the sequence controller 23, andthe sequence controller 23 controls the power source 18 so the currentis reduced for the pilot arc and increased for the main arc.

In the present invention, the sequence controller 23 divides the supplyof current into three stages from beginning to end while the main arc isbeing generated and increases the current incrementally. In dividing themain arc current into three stages, the sequence controller 23 performscontrol operations so the main arc in the first step is a small-currentarc effective at removing oil from the surface and surroundings of thesection of the base material to be melted, the main arc in the secondstep is an intermediate-current arc for melting the tip of the stud andthe section of the base material to be melted and for keeping the areaof the section of the base material to be melted within a predeterminedrange, and the main arc in the third step is a large-current arc formelting the tip of the stud and the section of the base material to bemelted into each other deeply.

The control output from the sequence controller 23 does not have to beinputted to the power source 18. It can also be inputted to a lift coilcontroller 25 for turning the lift coil 15 on and off. The lift coilcontroller 25 turns on the lift coil 15 to lift the collet 13 in thewelding gun 17 against resistance from an internal spring and raise thestud 11 a specific height with respect to the base material 14 and holdthe stud there while the pilot arc is generated and the stronger mainarc is generated. After the main arc has properly welded the tip of thestud 11 and the section of the base material 14 to be welded, thesequence controller 23 turns off the current to the lift coil 15 forbringing the stud 11 into contact with the base material 14 forcibly.When the power is turned off, the collet 13 is lowered by the springaction of the internal spring, and the stud 11 is brought into contactwith the base material 14 forcibly.

FIG. 4 is a detailed depiction of the stud 11 used in the presentinvention. The stud 11 is made from aluminum or an aluminum alloy. It isa T stud with a large-diameter head 26 and a rod-shaped shaft. In orderto be welded in the same manner as the iron-based stud 1 in FIG. 2, forexample, the head 26 has a diameter of 5 mm and the shaft 27 has adiameter of 3 mm. The length of the shaft 27 before welding is 3.3 to3.7 mm, or 0.3 to 0.7 mm longer than the iron-based stud 3 in FIG. 2.This allows for welding with the base material deep enough to obtain theappropriate welding strength. The tip 29 of the shaft 27 on the stud 11is conical with a flat end. The tip surface 30 is flat with a 1.5 mm to2 mm diameter, and the tapering angle α of the conical section isbetween 5 and 10°. The formation of a cone with a flat end concentratesthe arc in the center, keeps the reinforcement from tilting to one side,and keeps the height of the reinforcement from getting shorter. Byforming the tip 29 of the aluminum-based stud 11 of the presentinvention in this manner, the height of the stud 1 below the neck afterbeing welded is about 2.6 mm, the reinforcing height (h) of thereinforcement is less than 1 mm, and the diameter (d) of thereinforcement is less than 5 mm. As a result, the welding strength is ashigh as the iron-based stud shown in FIG. 2.

The following is an explanation of the operation of the stud weldingdevice 10 in the present invention with reference to FIG. 5(A) through(C). When a welding start signal is sent to the sequence controller 23in the control device 19 from the switch (not shown), theconstant-voltage pilot arc current is supplied from the power source 18to the aluminum-based stud 11 and the aluminum-based base material 14 inthe initial stage denoted by Phase I in FIG. 5(A). A signal is also sentto the lift coil controller 25, the lift coil 15 is activated, and thestud 11 is gradually lifted off the base material 14 against theresistance acting on the collet 13 as shown in FIG. 5(B). Once lifted,the pilot arc is generated. The stud 11 is kept at a specific height fora specific period of time. When the stud 11 is lifted from the basematerial 14, as shown in FIG. 5(C), a constant-level arc voltage isgenerated between the stud 11 and the base material 14. This is detectedby the voltage detector 21 and sent to the sequence controller 23. Thesequence controller 23 then makes sure the stud 11 is lifted off thebase material 14.

After the pilot arc has been generated, the sequence controller 23increases the current and supplies the main arc current from the powersource 18 in the first stage to the stud in the second phase denoted byPhase 11 in FIG. 5(A). The main arc current in the first stage is set ata small-current arc effective enough at removing oil from the surfaceand surroundings of the section of the base material 14 to be melted.When performing the welding in an inactive gas atmosphere, the watercomponent is scattered and does not contaminate the section of the studto be melted. The small-current arc in the first stage is effectiveenough to perform pre-welding processing.

Next, the sequence controller 23 increases the current from the powersource 18 and supplies the main arc current in the second stage to thestud 11 in the third phase denoted by Phase III in FIG. 5(A). The mainarc current in the second stage welds the tip 29 of the stud 11 and thesection of the base material 14 to be welded. This intermediate-currentarc keeps the area of the section of the base material 14 to be meltedwithin a predetermined range and positions the section to be melted withhigh precision.

In the fourth phase denoted by Phase IV after the third phase denoted byPhase III in FIG. 5(A), the sequence controller 23 increases the currenteven more and supplies the main arc current in the third phase from thepower source 18 to the stud 11. The main arc current in the third stageis large enough to perform deep welding on the tip of the stud 11 andthe section of the base material 14 to be welded. This is sufficient toweld the sections to be welded. The sequence controller 23 has areference table stored in RAM or ROM memory containing data related tothe welding of various types of studs and base materials. In Phases I,II, III and IV, the sequence controller 23 uses the signals from thevoltage detector 21 indicating the stud 11 has been lifted as theinitiation signals, and sets the proper timing and current levelsaccordingly. The power source 18 is a chopper high-frequency powersource. The size of the current outputted is controlled by signals froman external source using pulse wave modulation (PWM). Therefore, thesequence controller 23 can set the appropriate pilot arc current andmain arc current for the various stages and the appropriate length oftime for the various stages based on the type of stud and base materialbeing used.

When the third main arc in Phase IV is terminated, the main arc currentfrom the power source 18 is stopped. In the present invention, thesequence controller 23 operates the lift coil controller 25 so themolten tip of the stud is forcibly brought into contact with the moltensection of the base material to be welded in under 5 milli-seconds.Because the sequence controller 23 can check the reference table todetermine when to end Phase IV (the third main arc stage), the currentto the lift coil Is stopped at the appropriate time before the end ofthe process, and a signal is sent to the lift coil controller 25 toforcibly bring the tip of the stud 11 into contact with the moltensection of the base material 14 to be welded in under 5 milliseconds inPhase IV or after the third main arc stage has ended. In the presentinvention, the amount of time in which the tip of the stud is broughtinto contact with the base material is shortened, and the short currentis limited to a brief period of time. Because the short current isbrief, the splattering of molten metal is reduced by the pinch effect (aphenomenon in which the large current flowing through the molten fluidconstricts the fluid, the constriction reduces the flow and lessens theconstriction, and the lessening of the constriction once againconstricts the molten fluid). In testing, the period of forcible contactwas conducted within 0 and 4 milliseconds of ending the current. Thissignificantly reduced the amount of splattering of molten metal.

The time T in FIG. 5(B) is the range of time in which the tip of thestud is brought forcibly into contact with the base material after themain arc current has been terminated. After Phase IV in FIG. 5(A), thecurrent does not go down to zero immediately after the current is cut.Because some power remains in the circuit for supplying power to thestud 11 and the base material 14, the current cutoff time is denoted bydotted line 33 in the Figure. A stud contact signal from the sequencecontroller 23 is sent to the lift coil controller 25 during time 34 inFIG. 5(B) before the time 30 the current is cut. When the stud makescontact, the arc voltage in FIG. 5(C) goes to zero. This is detected bythe voltage detector 21. The sequence controller 23 receives the signalsfrom the voltage detector 21 and begins the contact timing.

When an aluminum or aluminum alloy stud 11 is forcibly brought intocontact with an aluminum or aluminum alloy base material 11, as shown inFIG. 2, the welding obtained is similar to that of a iron-based studwelded to an iron-based base material. In testing, the height of thealuminum-based stud 11 below the neck was about 2.6 mm, the reinforcingheight (h in FIG. 2) of the reinforcement 6 was less than 1 mm, and thediameter (d in FIG. 2) of the reinforcement was less than 5 mm. A highwelding strength was also maintained.

Because, in the present invention, the main arc current is divided intostages and increases incrementally in this welding method, the weldingarea of the section of the base material to be melted is kept within thedesired range when the tip of the stud is being welded to the section ofthe base material to be melted, the tip of the stud and the section ofthe base material to be melted are melted into each other deeply, andthe heat introduced to the stud and base material remains constant.Because the tip of the stud is applied under pressure to the basematerial in less time and the short current is controlled during thistime, the splattering of molten metal is reduced by the pinch effect (aphenomenon in which the large current flowing through the molten fluidconstricts the fluid, the constriction reduces the flow and lessens theconstriction, and the lessening of the constriction once againconstricts the molten fluid). This stabilizes the stud after welding atthe desired height below the neck, keeps the height of the studreinforcement and the diameter of the section to be welded within theappropriate ranges, and maintains a high welding strength. In addition,the aluminum-based stud is a T stud consisting of a large-diameter headand a rod-shaped shaft, and the profile of the end of the shaft isconical with a flat tip. As a result, the arc is concentrated in thecenter, the reinforcement does not tilt to one side, and the height ofthe reinforcement is kept from getting shorter.

The preferred weld parameters for the present invention are shown inFIG. 6. The weld parameters are first shown for different materials usedwith the previously disclosed T-stud. For example, when A7N01 is usedfor the base material 14 and A5056 is used for the stud 11, the weldcurrent voltage is maintained at 18 volts, the lift height is maintained(for the lift motor or coil position relative to the workpiece althoughthe welded tip may actually change as melting occurs) at 2.3millimeters, the step 1 welding current average is maintained about 100amps for about 20 milliseconds, the subsequent step 2 welding currentaverage is maintained about 170 amps for about 10 milliseconds, and thesubsequent step 3 welding current average is maintained about 290 ampsfor about 13 milliseconds. The final group of weld parameters are shownfor a T5 Christmas (“Xmas”) Tree style weld stud. The shape of this typeof stud is disclosed in U.S. Pat. No. 5,461,209 entitled “Stud Bolt”which issued to Yamada et al. on Oct. 24, 1995, and is incorporated byreference herein.

Various aspects of the present invention have been disclosed but otherembodiments can be used. For example, the preferred method and devicecan be used for weld studs which have differing shapes, such as thosewithout a T-shaped or enlarged head, although some of the advantages maynot be achieved. Furthermore, the stage timing, volts, amps anddistances can be varied depending upon the specific stud and basematerial dimensions and materials utilized. While various materials anddimensions have been disclosed, it will be appreciated that othermaterials and dimensions may be readily employed. It is intended by thefollowing claims to cover these and any other departures from thedisclosed embodiments which fall within the true spirit of thisinvention.

1. A welding method comprising: (a) an aluminum or aluminum alloy studbeing brought into contact with an aluminum or aluminum alloy basematerial, the stud having a cylindrical shaft and a welding end with asubstantially flat tip; (b) voltage being applied between the stud andthe base material; (c) the stud being lifted slightly off the basematerial; (d) a pilot arc with a small amount of current beinggenerated; (e) the main arc with a large amount of current beinggenerated; (f) melting the tip of the stud and the section of the basematerial to be melted; (g) pressuring the molten tip of the stud againstthe molten base material in under five milliseconds after the main arccurrent has been cut off; (h) the end serving to centrally concentratethe main arc; and (i) welding together the stud and the base material.2. The welding method of claim 1 wherein the stud is a T stud consistingof a large-diameter head and a smaller-diameter, rod-shaped shaft. 3.The welding method of claim 2 wherein a profile of the end of the shaftis conical with a substantially flat tip adjacent an enlarged portion ofthe conical end.
 4. The welding method of claim 1 further comprisingincrementally increasing current for the main arc into at least threesteps, wherein the main arc in the first step is a small-current arceffective at removing oil from the surface and surroundings of thesection of the base material to be melted, the main arc in the secondstep is an intermediate-current arc for melting the tip of the stud andthe section of the base material to be melted and for keeping the areaof the section of the base material to be melted within a predeterminedrange, and the main arc in the third step is a large-current arc formelting the tip of the stud and the section of the base material to bemelted into each other deeply.
 5. The welding method of claim 1 whereinthe stud has, a substantially conical shape adjacent the welding end,the conical shape and end serving to centrally concentrate the main arc.6. The welding method of claim 1 wherein steps (a) through (h) areperformed substantially in sequential order.
 7. The welding method ofclaim 1 wherein: (i) the weld current voltage is about 18–24 volts andthe weld current is about 100–900 amps for about 5–20 millisecondsduring a first period; (j) the weld current voltage is substantiallyunchanged and the weld current is increased to about 170–900 amps forabout 5–10 milliseconds during a subsequent second period; and (k) theweld current voltage is substantially unchanged and the weld current isincreased to about 260–1200 amps for about 5–13 milliseconds for asubsequent third period.
 8. A welding method comprising: (a) contactinga stud with a base; (b) applying voltage between the stud and the base;(c) lifting the stud off the base; (d) generating an arc; (e) meltingthe tip of the stud and a section of the base; (f) applying pressure tothe tip of the stud and the section of the base that has been melted;(g) dividing a main welding current into at least three stages andincrementally increased the welding current from the beginning stage tothe end stage while maintaining the voltage substantially constant; and(h) welding together the stud and base; wherein the stud is aluminum oraluminum alloy.
 9. The welding method of claim 8 wherein the stud is a Tstud consisting of a large-diameter head and a smaller-diameter,rod-shaped shaft.
 10. The welding method of claim 9 wherein a profile ofthe end of the shaft is conical with a flat tip.
 11. The welding methodof claim 8 wherein the base is aluminum or an aluminum alloy.
 12. Thewelding method of claim 8 wherein the stud has a cylindrical shaft, asubstantially conical end extends from the shaft and a flat tip is onthe conical end opposite the shaft.
 13. The welding method of claim 8further comprising moving the molten tip of the stud against the moltenbase in under five milliseconds after the arc current has been cut off.14. The welding method of claim 8 further comprising incrementallyincreasing current for the main arc into at least three steps, whereinthe main arc in the first step is a small-current arc effective atremoving oil from the surface and surroundings of the section of thebase to be melted, the main arc in the second step is anintermediate-current arc for melting the tip of the stud and the sectionof the base to be melted and for keeping the area of the section of thebase to be melted within a predetermined range, and the main arc in thethird step is a large-current arc for melting the tip of the stud andthe section of the base to be melted into each other deeply.
 15. Thewelding method of claim 8 wherein: (i) the weld current voltage is about18–24 volts and the weld current is about 100–900 amps for about 5–20milliseconds during a first period; (j) the weld current voltage issubstantially unchanged and the weld current is increased to about170–900 amps for about 5–10 milliseconds during a subsequent secondperiod; and (k) the weld current voltage is substantially unchanged andthe weld current is increased to about 260–1200 amps for about 5–13milliseconds for a subsequent third period.
 16. The welding method ofclaim 8 wherein steps (a) through (h) are performed substantially insequential order.
 17. A welding system comprising: an aluminum oraluminum alloy stud; a base; a first device operably applying voltagebetween the stud and the base; and a second device operably lifting thestud slightly off the base; wherein a pilot arc with a small amount ofcurrent is generated, a main arc with a large amount of welding currentis generated, and the tip of the stud and the section of the base aremelted; wherein pressure is applied to the tip of the stud and thesection of the base that has been melted; wherein the welding current isdivided into stages from beginning to end and increased as the main arcis generated; wherein the molten tip of the stud is applied underpressure to the molten base in under five milliseconds after the mainarc current has been terminated; and wherein the stud and base areoperably welded together.
 18. The welding system of claim 17 wherein thestud is a T stud including a large-diameter head and a smaller-diameter,rod-shaped shaft.
 19. The welding system of claim 18 wherein a profileof the end of the shaft is substantially conical with a flat tip. 20.The welding system of claim 17 wherein the base is aluminum or analuminum alloy.
 21. The welding system of claim 17 wherein the stud hasa cylindrical shaft, a substantially conical end extends from the shaftand a flat tip is on the conical end opposite the shaft.
 22. The weldingmethod of claim 17 wherein: (i) the welding current voltage is about18–24 volts and the weld current is about 100–900 amps for about 5–20milliseconds during a first period; (j) the welding current voltage issubstantially unchanged and the weld current is increased to about170–900 amps for about 5–10 milliseconds during a subsequent secondperiod; and (k) the welding current voltage is substantially unchangedand the weld current is increased to about 260–1200 amps for about 5–13milliseconds for a subsequent third period.
 23. The welding system ofclaim 17 wherein there are three welding current stages and the main arcin the first stage is a small-current arc effective at removing oil fromthe surface and surroundings of the section of the base to be melted,the main arc in the second stage is an intermediate-current arc whichoperably melts the tip of the stud and the section of the base, and themain arc in the third stage is a large-current arc which operably meltsthe tip of the stud and the section of the base.
 24. A welding systemcomprising: an aluminum or aluminum alloy stud being a T stud includinga large-diameter head, a smaller-diameter, rod-shaped shaft and asubstantially conical shaft section adjacent a substantially flat tip;an aluminum or aluminum alloy base; and a welding device operable toweld the stud to the base; wherein a pilot arc with a small amount ofcurrent is generated, the main arc with a large amount of weldingcurrent is generated, and the tip of the stud and the section of thebase are melted; wherein pressure is applied to the tip of the stud andthe section of the base that has been melted; wherein the weldingcurrent is divided into stages from beginning to end and incrementallyincreased as the main arc is generated: (a) the welding current voltagebeing about 18–24 volts and the weld current is about 100–900 amps forabout 5–20 milliseconds during a first period; (b) the welding currentvoltage being substantially constant and the weld current is increasedto about 170–900 amps for about 5–10 milliseconds during a subsequentsecond period; and (c) the welding current voltage being substantiallyconstant and the weld current is increased to about 260–1200 amps forabout 5–13 milliseconds for a subsequent third period; and wherein thestud and base are operably welded together.
 25. The welding system ofclaim 24 wherein there are three welding current stages and the main arcin the first stage is a small-current arc effective at removing oil fromthe surface and surroundings of the section of the base to be melted,the main arc in the second stage is an intermediate-current arc whichoperably melts the tip of the stud and the section of the base, and themain arc in the third stage is a large-current arc which operably meltsthe tip of the stud and the section of the base.
 26. The welding systemof claim 24 wherein the molten tip of the stud is applied under pressureto the molten base in under five milliseconds after the main arc currenthas been terminated.